This invention relates to apparatus for pulverizing, i.e., grinding, material, and more specifically to an inerting and fire extinguishing system that is particularly suited for employment in a pulverizing bowl mill wherein the inerting and fire extinguishing system is operative to inert a hazardous condition which may be present therewithin and/or to extinguish a fire that may be burning therewithin.
It has long been known in the prior art to provide apparatus employable for purposes of effecting the grinding of materials. More specifically, the prior art is replete with examples of various types of apparatus that have been used heretofore to effect the grinding of a multiplicity of different kinds of materials. In this regard, in many instances discernible differences of a structural nature can be found to exist between individual ones of the aforesaid apparatus. The existence of such differences is, in turn, attributable for the most part to the diverse functional requirements that are associated with the individual applications in which such apparatus are designed to be employed. For instance, in the selection of the particular type of apparatus that is to be utilized for a specific application, one of the principal factors to which consideration must be given is that of the nature of the material that is to be in the apparatus. Coal is one such material wherein there is a need to grind it in order to render it suitable for use in certain applications. Furthermore, fossil fuel fired power generation systems represent one such application in which it is desired to employ coal, as the source of fuel therefor, and wherein a requirement exists to grind, i.e., pulverize the coal to render it suitable for use for this purpose, i.e., for use in a coal-fired power generation system.
For purposes of the discussion that follows, the coal-fired power generation systems referred to above are considered to consist of essentially the following major operating components: a coal feeder, apparatus for pulverizing coal, a distribution system for distributing the coal after the pulverization thereof, a furnace in which the coal is to be burned and the requisite controls for effecting the proper operation of the coal-fired power generation system. Of particular interest herein is that portion of the coal-fired power generation system which has been identified above as the apparatus for pulverizing the coal. Coal pulverizing apparatus are not new. They have been known to exist in the prior art for more than half a century. Furthermore, many improvements in the construction and/or mode of operation of coal pulverizing apparatus have been made during this period.
There are a number of features that it is advantageous for any coal pulverizing apparatus to possess, but particularly those which are designed for employment in a coal-fired power generation system. Reference is had here to features such as reliability, low power consumption, minimum maintenance and wide range of capacity. In addition, such apparatus advantageously should also be characterized by quiet operation, integrated lubrication systems, convenient adjustment and control of coal flow and fineness, and the ability to handle the high temperature air that is required for high moisture coal.
One particular type of coal pulverizing apparatus which is to be found in the prior art that is advantageously characterized by the embodiment therein of the above-recited features is an apparatus most commonly referred to in the industry by the name bowl mill. The latter apparatus obtains its name by virtue of the fact that the pulverization, i.e., grinding, of the coal which takes place therein is effected on a grinding surface that in configuration bears a resemblance to a bowl.
Reference may be had, by way of exemplification, to U.S. Pat. No. 3,465,971, the latter being assigned to the same assignee as the instant application, for a teaching of the nature of the construction and the mode of operation of a prior art form of bowl mill that is suitable for use in a coal-fired power generation system to effectuate the pulverization of the coal that is to be burned as fuel therein. As taught by the aforementioned patent, a bowl mill essentially consists of a body portion in which a grinding table is mounted for rotation, a plurality of grinding rollers that coact with the grinding table to effect the grinding of coal interposed therebetween, coal supply means for feeding to the interior of the bowl mill the coal that is to be pulverized, and air supply means for supplying to the interior of the bowl mill the air required in the operation of the latter. In accordance with the mode of operation of such a bowl mill, the coal, which enters the bowl mill, is pulverized by virtue of the coaction of the grinding rollers with the grinding table. After being pulverized, the coal particles are thrown outwardly by centrifugal force whereby the particles are fed into a stream of air that is entering the bowl mill. The stream of air, which now contains pulverized coal particles, flows through a tortuous path that is established in part by the positioning within the bowl mill of a suitably supported deflector means. As the stream of air and coal particles flows along the aforementioned tortuous path, the sharp turns contained therein effects the separation of the coarse coal particles from the air stream. These coarse coal particles are then suitably returned to the grinding table for further pulverization, while the fine coal particles are carried through the bowl mill in the air stream, and exit therefrom along with the air.
In a conventional coal-fired power generation system, a multiplicity of bowl mills of the type shown in the aforementioned patent would commonly be employed for purposes of satisfying the requirements of the system for pulverized coal. By way of example, the capacity of each of the individual bowl mills might be on the order of one hundred tons per hour of coal.
Although bowl mills constructed in accordance with the teachings of the aforementioned patent have, under actual operating conditions, proven capable of providing adequate performance to date, a need has nevertheless been evidenced for improvements to be made therein. More specifically, prolonged operation of this type of bowl mill has revealed the existence of several conditions of an undesirable nature that can arise during the use thereof. In particular, reference is had here to the fact that it is known that on occasion a hazardous condition may be found to exist where if the hazardous condition is not obviated the possibility exists that the hazardous condition may eventually give rise to the occurrence of an explosion in the bowl mill. Secondly, should a fire occur therewithin if not rapidly extinguished, it could spread to other components of the coal-fired power generation system besides just the bowl mill. Moreover, in view of the relatively high temperatures that are required for purposes of the operation of the bowl mill, fires have been known to occur notwithstanding the fact that no explosion has taken place. A need has, therefore, been evidenced in the prior art for a system that would be suitable for installation in a bowl mill, and which would be operative both to provide an inert atmosphere within the bowl mill whenever a hazardous condition is found to be present therein such as to reduce the potential that an explosion will occur in the bowl mill and to enable a fire to be safely controlled should a fire be detected somewhere within the segment of the coal-fired power generation system that encompasses the bowl mill.
It is, therefore, an object of the present invention to provide a new and improved inerting subsystem suitable for use in a bowl mill of the type that is operative for purposes of effecting the pulverization of a material such as coal.
It is a further object of the present invention to provide a new and improved fire extinguishing subsystem that is suitable for use in combination with the subject inerting subsystem in a bowl mill of the type that is operative for purposes of effecting the pulverization of a material such as coal.
It is another object of the present invention to provide such a combination inerting and fire extinguishing system particularly suited for use in a bowl mill which embodies a continuous purging means that is operative during any inerting sequence to cause an inerting medium to flow continually through the bowl mill so as to ensure that there is no buildup of volatile gases within the bowl mill.
It is still another object of the present invention to provide such a combination inerting and fire extinguishing system particularly suited for use in a bowl mill which embodies a backup inerting means that is operative to provide CO.sub.2 inerting when the primary steam inerting system is either not available or for some other reason cannot be utilized.
A further object of the present invention is to provide such a combination inerting and fire extinguishing system particularly suited for use in a bowl mill which embodies a bowl mill clearing means that is operative after the bowl mill has been taken off line to clear the bowl mill of its contents via a steam flow so as to render the bowl mill ready for restart.
A still further object of the present invention is to provide such a combination inerting and fire extinguishing system particularly suited for use in a bowl mill which embodies a water injection fire suppression means that is operative in the event of a fire in the bowl mill to accomplish the injection thereto of water simultaneous with a steam clearing of the interior of the bowl mill.
Yet a further object of the present invention is to provide such a combination inerting and fire extinguishing system particularly suited for use in a bowl mill that is capable of either manual operation or automatic operation.
Yet another object of the present invention is to provide such a combination inerting and fire extinguishing system which is suitable for employment in newly constructed bowl mills as well as being equally suitable for employment in retrofit applications.
Yet still another object of the present invention is to provide such a combination inerting and fire extinguishing system particularly suited for use in a bowl mill which is advantageously characterized both by its ease of manufacture and its ease of installation in a bowl mill, while yet being relatively inexpensive to provide.